Lead readily crosses the placental barrier and concentrates in the developing infant's organs where it may damage the developing nervous system. The primary objective of the research under this contract is to investigate the relative contribution to the infant in utero of mother's current environmental lead compared with mobilization of lead from maternal stores, especially bone lead. Investigating the stable lead isotopic profile (i.e., ratio of 204/206/207 and 208 lead) of environmental lead exposures concurrent with pregnancy, and contrasting these lead profiles with those of lead exposures that occurred earlier in the pregnant woman's life makes it possible to separate lead sources. Such profiles may be distinctly characteristic of particular geographic locations, as occurs at several locations in Australia; e.g., Port Pirie and Tasmania. It is possible to differentiate whether the lead reaching the fetus is coming predominately from current sources or previous body stores. In Phase I of this work, the isotopic profile of stable lead in these Australian locations will be characterized and the number of women ages 20-35 who move between these locations will be determined. If isotopic ratios are sufficiently different given the number of women potentially available as subjects, Phase II will investigate the biokinetics of lead during pregnancy to determine the source of lead to the developing infant. The infants will also be evaluated during the first six months of life to determine the contribution of maternal lead sources for the infant.